University  of  California— College  of  Agriculture, 

AGRICULTURAL  EXPERIMENT  STATION. 

E.  W.  HILGARD,  Director. 


THE  POTATO-WORM  IN  CALIFORNIA 


(Gelechia  operculella,  Zeller.) 


By  WARREN  T.  CLARKE. 


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INFESTED  TUBER. 

BULLETIN  No.  135 

(Berkeley,  October,  1901.) 


A.   J.   JOHNSTON, 


SACRAMENTO: 
:    :    :    superintendent  state  printing. 
.      1901. 


EXPERIMENT  STATION  STAFF. 


E.  W.  HILGARD,  Ph.D.,  LL.D.,  Director  and  Chemist. 

E.  J.  WICKSON,  M.A.,  Horticulturist  and  Superintendent  of  Agricultural  Grounds. 

R.  H.  LOUGHRIDGE,  Ph.D.,  Agricultural  Geologist  and  Chemist. 

C.  W.  WOODWORTH,  M.S.,  Entomologist. 

W.  A.  SETCHELL,  Ph.D.,  Botanist. 

M.  E.  JAFFA,  M.S.,  First  Assistant  Chemist,  Agricultural  Laboratory. 

GEORGE  E.  COLBY,  M.S.,  Second  Assistant  Chemist,  Agricultural  Laboratory. 

FREDERIC  T.  BIOLETTI,  M.S.,  Bacteriologist  and  Foreman  of  Viticultural  Cellar. 

J.  BURTT  DAVY,  Assistant  Botanist. 

LEROY  ANDERSON,  M.S.A.,  Dairy  Husbandman. 

A.  R.  WARD,  B.S.A.,  D.V.M.,  Veterinarian. 

E.  H.  TWIGHT,  Assistant  in  Viticulture. 

CHARLES  H.  SHINN,  A.B.,  Inspector  of  Stations. 

C.  A.  COLMORE,  Clerk  to  Director. 

EMIL  KELLNER,  Foreman  of  Central  Station  Grounds. 


J 

>  Coast  Range  Substation,  Paso  Robles. 


JOHN  TUOHY,  Patron, 

'  £  Tulare  Substation,  Tulare. 

JULIUS  FORRER,  Foreman, 

R.  C.  RUST,  Patron, 

}  Foothill  Substation,  Jackson. 
JOHN  H.  BARBER,  Foreman, 

S.  D.  MERK,  Patron, 

3.  W.  NEAL, 

S.   N.  ANDROUS,  Patron,  )  „  „  ,..       .     „   ,       ,.        (Pomona. 

>  Southern  California  Substation,  <  „ 
J.  W.  MILLS,  Foreman,       )  (  Ontario. 

V.  C.  RICHARDS,  Patron,  i  „      . 

T    ^^rTTTWT^„    .  >  Forestry  Station,  Chico. 

T.  L.  BOHLENDER,  in  charge,  S  * 

ROY  JONES,  Patron,        )  „  n      .  „     . 

...  .    ^„„ „  t  Forestry  Station,  Santa  Monica. 

WM.   SHUTT,  Foreman,  S  J 


TABLE  OF  CONTENTS. 


Page. 

NOTE  BY  THE   PROFESSOR  OF  ENTOMOLOGY 5 

INJURIOUS  NATURE  OF  THE  POTATO-WORM .. 5 

BIBLIOGRAPHY.. 6 

GENERAL  DESCRIPTION.... 8 

The  egg  and  oviposition _ _ 9 

The  larva. _ _ ._ 10 

The  chrysalis  and  pupation _ _ 11 

LIFE  HISTORY 12 

CHARACTER  OF  INJURY 14 

MODES  OF  INFECTION 15 

By  infection  of  the  stem 15 

By  direct  infection  of  the  tuber  in  the  hill _ 15 

Direct  infection  after  digging 16 

Indirect  infection  after  digging ._ _ 16 

Infection  in  the  sack  or  bin  ._ _ 16 

EXPERIMENTS  IN  THE  FIELD  AND  STOREROOM 16 

Field  experiments ^_. 17 

Storage  experiments _ 21 

Experiments  with  Carbon  Bisulfid _ _ 23 

REMEDIES 24 

Food  plants  should  be  destroyed _ 25 

Light-trapping _ 25 

Destroy  infested  stalks 25 

Careful  hilling 26 

Avoid  exposure  while  digging  the  potatoes 26 

Clean  up  the  field  after  digging 27 

Control  of  the  moth  among  stored  potatoes ___ 27 

OTHER  PESTS. 28 

Flea  Beetles 29 

Stenopelmatus _ _ 29 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/potatowormincali135clar 


THE  POTATO-WORM  IN  CALIFORNIA. 

(Gelechia  operculella,  Zeller.) 


By  WARREN  T.  CLARKE. 


Note.— The  present  paper  has  been  prepared  in  accordance  with  the  policy  of 
permitting  properly  qualified  students  of  the  Agricultural  Department  to  take 
part  in  the  actual  work  of  the  Experiment  Station.  The  insect  treated  is  prob- 
ably the  most  injurious  species  attacking  truck  crops  in  the  State,  but  has 
hitherto  received  but  little  attention  by  entomologists.  The  study  here  re- 
ported constitutes  a  very  material  advance  in  our  knowledge  of  the  life  history 
and  habits  of  the  insect  and  of  the  problem  of  its  control. 

C.  W.  Woodworth,  Entomologist. 


The  most  serious  potato  pest  in  California  is  the  potato-worm  ( Gelechia 
operculella,  ZelL),  a  widely  distributed  insect  also  known  in  the  Southern 
States  as  the  Tobacco  Leaf  Miner  or  Split-worm. 

The  damage  to  the  potato  crop  in  California,  as  estimated  by  the 
writer  on  the  basis  of  opinions  obtained  from  a  large  number  of  growers 
and  dealers,  aggregates  in  some  years  fully  twenty-five  per  cent. 

In  one  section  where  some  of  the  finest  of  potatoes  are  grown,  the 
Salinas  Valley,  the  dealers  estimate  that  at  times  the  loss  has  gone  as 
high  as  40,000  sacks  in  a  single  year,  and  indeed  the  potatoes  from  any 
section  of  the  State  have  to  be  watched  carefully  by  the  dealers  to  avoid 
wormy  lots.  This  need  of  care  is  because  of  the  fact  that  a  very  few 
wormy  potatoes  may  infect  in  a  few  weeks  a  whole  storeroom  full  of 
what  were  originally  clear  tubers.  As  the  potato  is  a  food  product  that 
is  expected  to  retain  its  value  for  many  months,  this  possibility  of 
infestation  becomes  a  most  serious  question.  Certain  rots,  particularly 
that  produced  by  a  species  of  Penicillium*,  follow  the  work  of  the 
worm,  starting  in  the  burrow  filled  with  excrement  and  ultimately 
involving  the  whole  tuber. 

Potatoes  for  the  Philippine  and  Hawaiian  trade  require  very  careful 
culling  before  shipping,  because  the  warm,  moist  conditions  on  the 
voyage  into  the  tropics  favor  both  the  insect  and  the  fungus,  a  single 
infested  potato  often  spoiling  a  whole  crate. 

The  injury  to  the  plant  in  the  field,  though  not  as  large  in  the  aggre- 
gate as  that  to  the  potatoes  in  storage,  occasionally  results  in  the  total 
loss  of  the  crop. 


*  Specimens  examined  by  Mr.  O.  Butler,  of  this  laboratory,  show  the  presence  of  a  red 
yeast,  a  species  of  Mucor,  and  of  Penicillium,  this  latter  distinctly  predominating. 


—  6  — 

The  cause  of  this  loss  is  not  generally  recognized  by  the  grower,  who 
commonly  designates  it  as  a  "mould,"  "rust,"  or  "fungus."  While  it 
is  difficult  to  deal  with  in  the  field,  yet  it  can  be  controlled  even  there. 
This  failure  to  recognize  the  cause  has  been  an  important  factor  in  the 
spread  of  the  trouble. 

The  injury  produced  by  the  worm  is  extremely  evident  to  the  house- 
keeper and  is  well  known  to  all  dealers  in  potatoes;  but  very  generally 
they  do  not  understand  the  nature  of  the  insect  producing  the  trouble. 

Among  the  commonest  misconceptions  may  be  mentioned  the  idea 
that  it  is  a  form  of  rot  not  associated  with  any  insect.  Usually,  how- 
ever, the  work  of  the  worm  is  recognized  as  such,  but  its  connection 
with  any  other  stage  of  existence  is  unknown  or  misunderstood.  The 
importance  of  knowledge  on  this  subject  rests  on  the  fact  that  the  care- 
lessness of  a  grower  or  dealer  stands  as  a  constant  menace  to  all  the 
potatoes  in  the  neighborhood. 

Though  the  potato-worm  is  so  injurious  in  California,  and  occurs  in 
the  East  and  in  many  parts  of  the  old  world,  it  appears  to  be  quite 
unknown  in  any  of  the  adjacent  States,  or  at  least  does  not  appear  in 
sufficient  number  to  cause  any  marked  damage.  The  Station  entomolo- 
gists of  Arizona,  Nevada,  and  Oregon  each  have  written  us  that  the 
insect  has  not  come  to  their  personal  notice. 

The  insect  has  long  been  known  to  be  greatly  injurious  to  solanaceous 
plants,  and  has  been  described  by  various  authors  under  various  names. 
In  all  cases  where  the  food  habit  has  been  noted,  however,  it  has  been 
found  to  be  working  on  some  one  of  the  Solanacese,  and  in  no  case  on 
plants  of  any  other  family.  This  restriction  of  an  insect  to  one  food- 
plant  is  very  common,  and  in  the  present  case  at  least  simplifies  the 
work  of  control,  but  also  opens  the  way  for  its  preservation  in  the  wild 
plants  of  the  favored  family.  We  find  the  insect  in  many  cases  doing  great 
damage  to  the  tobacco  plant  (see  U.  S.  Dept.  of  Agric.  Farmers'  Bulle- 
tin No.  120,  etc.),  and  it  is  as  a  tobacco  pest  that  it  has  been  most  noted 
in  this  country.  Its  work  in  California,  however,  is  on  the  potato,  and 
this  bulletin  is  confined  to  its  damage  to  that  plant. 

Bibliography. — The  insect  was  first  described  by  Zeller  in  1873  in  his 
Beitrage  zur  Kenntniss  der  Nordamerikanischen  Nachtfalter,  62,  under 
the  name  Gelechia  operculella.  The  type  specimens  from  which  this 
description  was  made  were  received  from  Texas. 

In  November,  1874,  Boisduval  redescribed  the  insect  in  Jahrbuch 
Soc.  Cent.  Hort.,  under  the  name  Bryotropha  solanella.  He  noted  that 
it  caused  great  damage  to  potatoes  in  Algeria,  and  stated  that  the  eggs 
were  laid  upon  the  young  plant,  and  that  the  larvae  on  hatching  bur- 
rowed into  the  stem  and  then  down  and  through  the  tissue  of  the  stem 
into  the  tuber.     This  passing  of  the  larvse  through  the  stem  into  the 


tuber  is  probably  incorrect,  as  it  was  in  no  way  confirmed  by  the  pres- 
ent experiments. 

The  next  reference  made  to  the  insect  was  by  Ragonot,  in  1875,  in 
the  Bulletin  Soc.  Ento.  France,  5  (v),  pp.  xxxv-xxxvn,  in  which  he 
redescribed  the  insect  under  Boisduval's  original  name,  with  remarks 
upon  its  injuries. 

In  March,  1878,  V.  T.  Chambers,  of  Covington,  Ky.,  in  the  Canadian 
Entomologist,  Vol.  X,  pp.  50-54,  redescribes  the  insect  under  the  name 
Gelechia  solaniella,  and  notes  it  as  mining  the  leaves  of  Solatium  Caro- 
linense. 

In  1879,  Ragonot,  in  the  Bulletin  Soc.  Ento.  France,  pp.  cxlvi-cxlvii, 
again  described  the  insect  under  the  name  Gelechia  tabacella  as  a 
tobacco  pest. 

In  1880,  Meyrick,  in  an,  article  in  Proc.  Linn.  Soc,  New  South  Wales, 
Vol.  IV,  pp.  112-114,  treats  the  insect  as  a  potato  pest  under  the  name 
Gelechia  solanella. 

In  1883,  Matthew  Cooke,  in  his  book  "  Injurious  Insects  of  the  Orchard, 
Vineyard,  Field,  etc.,"  pp.  313-315,  notes  the  insect  as  having  been 
observed  by  him  in  California  as  early  as  1881.  He  states  that  "the 
moths  appear  about  the  first  of  July  and  deposit  their  eggs  in  potatoes 
after  the  latter  are  gathered  from  the  ground  and  placed  in  heaps  or 
sacks,"  and  recommends  close  covering  the  potatoes  after  digging  as  a 
preventive  of  infestation. 

In  1886,  Meyrick  makes  further  notes  on  Gelechia  solanella  in  Trans. 
New  Zealand  Institute,  Vol.  XVIII,  pp.  166-167. 

In  1889,  Mr.  Henry  Tryon,  in  his  Report  on  Insect  and  Fungous 
Pests,  pp.  175-181,  treating  of  the  insect  in  Queensland,  quotes  from  a 
correspondent  of  his,  Mr.  G.  Searle,  the  statement:  "The  uppermost 
potatoes,  those  which  are  nearest  the  surface,  are  of  course  most  easily 
reached,  nor  is  it  by  any  means  a  difficult  matter  for  the  insect  to  pene- 
trate .to  the  depth  of  three  or  four  inches  when  the  soil  is  open,  uncom- 
pressed, or  lumpy";  and  again,  "The  potatoes,  whilst  lying  exposed  in 
rows,  were  attacked  by  the  insects."  These  statements  are  worthy  of 
note,  because  of  their  economic  bearing,  and  they  were  fully  confirmed 
by  the  present  inquiry. 

In  September,  1892,  the  Government  Entomologist,  Mr.  A.  Sydney 
Olliff,  in  the  Agricultural  Gazette  of  New  South  Wales,  reports  the 
insect  as  a  tobacco  pest  in  that  colony. 

In  the  same  year,  Riley  and  Howard,  in  Insect  Life,  Vol.  IV,  Nos.  7 
and  8,  pp.  239-242,  figure  and  discuss  the  insect  quite  fully,  referring 
to  its  presence  in  California,  and  suggesting  that  it  might  have  been 
brought  by  Chinese  gardeners  from  China.  Under  the  head  of  reme- 
dies, "  the  immediate  destruction  of  the  infested  potatoes  "  is  urged,  as 
is  also  the  careful  packing  or  storing  of  the  sound  potatoes  in  tight 
rooms. 


—  8  — 

Again,  in  the  same  year,  Riley  discusses  the  insect  in  the  report  of 
the  Secretary  of  Agriculture,  pp.  156-157,  and  sounds  a  note  of  warning 
in  these  words:  "The  undue  presence  of  so  serious  a  pest  in  California 
calls  for  energetic  measures.  All  infested  potatoes,  wherever  found, 
should  be  immediately  destroyed,  and  receptacles  in  which  they  have 
been  stored  should  be  treated  with  kerosene.  Sound  potatoes  should  be 
stored  in  tight  rooms. "  This  is  good  advice  indeed,  but  since  it  has 
seldom  or  never  been  followed  the  pest  has  increased. 

The  only  other  reference  noted  is  an  article  by  Dr.  L.  O.  Howard,  in 
the  Department  of  Agriculture  Year  Book  for  1898,  pp.  137-140,  where 
the  insect  is  treated  of  as  a  tobacco  pest;  a  revised  reprint  of  which 
appears  in  U.  S.  Department  of  Agriculture  Farmers'  Bulletin  No.  120, 
pp.  19-22. 

The  above  (by  no  means  complete)  bibliography  of  the  insect  shows 
that  it  is  widespread  and  very  injurious  to  solanaceous  plants.  It  has 
been  described  from  different  parts  of  the  world  under  various  names, 
but  probably  Zeller's  naming,  G.  operculella,  holds,  on  account  of  priority. 

We  here  give  a  partial  synonymy  of  the  insect,  furnished  by  Lord 
Walsingham,  and  copied  from  the  U.  S.  Department  of  Agriculture 
Farmers'  Bulletin  No.  120,  p.  22: 

Solanella  Bdv. 

Gelechia  terella  (a  homonym),  Wkr.,  Cat.  Lp.  Ins.  B.  M.,  XXX,  1024  (1864).  Bryotro- 
pha  solanella  Bdv.,  J.  B.  Soc.  Cent.  Hort.  1874;  Rag.,  Bull.  Soc.  Ent.  Fr.,  1875,  XXXV- 
XXXVII.  Gelechia  tabacella  Rag.,  Bull.  Soc.  Ent.  Fr.,  1879,  CXLVI-CXLVII.  Gele- 
chia solanella  Meyr.,  Pr.  Lin.  Soc.  N.  S.  W.,  112  (1879);  N.  Z.  Jr.  Sc,  II,  590  (1885).  Lita 
tabacella  Rag.,  Bull.  Soc.  Ent.  Fr.,  1885,  CXI-CXII.  Gelechia  solanella  Meyr.,  Tr.  N.  Z. 
Inst.,  XVIII,  166-167  (1886).    Lita  solanella  (Olliff),  Agr.  Gaz.  N.  S.  W\,  II,  158-9  (1891). 

GENERAL    DESCRIPTION. 

The  nearest  relative  that  we  have  to  this  insect  that  is  injurious  to 
crops  is  the  peach-worm  (Anarsia  lineatella),  whose  ravages  are  well 
known  to  and  dreaded  by  the  peach-grower.  Both  this  insect  and  the 
potato-worm,  as  well  as  most  of  the  moths  belonging  to  this  family,  are 
of  small  size,  with  narrow,  well-fringed  wings;  very  delicate  and 
generally  of  quite  subdued  coloration. 

The  potato  moth  is  grayish-brown,  with  ochreous  tints  intermixed. 
Under  magnification  it  appears  to  be  dusted  over  with  white  and  black 
specks.  The  brown  and  ochre  of  the  anterior  wings  is  in  the  form  of 
more  or  less  regular  longitudinal  bands.  These  bands,  varying  in 
relative  size  in  different  specimens,  cause  a  certain  amount  of  variation 
in  color  to  appear.  The  general  color-effect  of  the  posterior  wings  is 
similar  to  but  lighter  than  that  of  the  anterior  wings.  Both  sets  of 
wings  are  well  fringed,  the  posteriors  having  longer  fringes  than  the 
anteriors.  The  antennae  are  rather  prominent,  and  are  inserted  just 
anterior  to  the  center  of  the  compound  eyes.     The  palpi  are  prominent, 


—  9 


Fig.  1.     Adult  moth  of  potato- worm  (Gelechia  operculella,  Zell.). 
Actual  size  shown  by  hair  line. 


gray-brown  externally  and  dusty  yellow  internally.  When  at  rest  the 
wings  are  folded  somewhat  roof-shape  over  the  abdomen,  and  when  in 
this  position  the  length  of  the  insect  is  about  8  mm.  (-£  in.).  With 
wings  expanded  the  insect  measures  from  tip  to  tip  16  mm.  (|  in.). 
The  illustrations  of 
the  insect  (Fig.  1) 
give  a  very  fair  idea 
of  its  general  appear- 
ance. Other  mem- 
bers of  the  group  dif- 
fer from  it  in  minute 
characters  that  would 
be  noted  by  an  ento- 
mologist, but  are  not 
found  in  the  same 
situations.  They  are 
quite  quick  flyers, and 
are  easily  recognized  in  storerooms  by  their  rapid  flight  toward  the 
light  when  they  are  disturbed.  The  female  is  somewhat  larger  and 
more  robust  than  the  male. 

The  Egg  and  Oviposition. — The  egg  is  about  \  mm.  in  diameter  and 
\  mm.  long.  It  is  of  an  oval  shape,  and  shows  under  the  magnifying 
glass  the  color-play  of  pearl,  its  general  color  being  a  shining  white.  Its 
extreme  minuteness  and  the  fact  that  it  is  placed  in  the  most  incon- 
spicuous positions  available 
render  it  difficult  of  detection. 
We  present  a  microphoto- 
graph  (see  Fig.  2)  of  a  num- 
ber of  the  eggs  in  situ  about 
the  eye  of  a  potato,  which 
gives  a  fair  idea  of  their  gen- 
eral appearance.  The  magni- 
fication is  twenty  diameters. 
The  female  depositing  these 
eggs  was  placed  in  a  jar  with 
one  thoroughly  cleaned  potato 
and  was  observed  in  the  act 
of  oviposition.  She  always 
sought  the  eye  of  the  potato 
as  the  place  to  lay  the  egg. 
Having  found  a  position  that 
seemed  to  suit  her,  she  settled  down  flat  on  the  surface  at  this  place, 
and  remained  quiet  for  two  or  three  minutes.  Then  a  drawing  of  the 
tip  of  the  abdomen  toward  the  thorax,  ventrally,  was  observed  and  the 


Fig.  2.    The  Egg.    Enlarged  twenty  diameters. 


—  10  — 

egg  was  extruded.  The  process  was  repeated  for,  in  one  case,  three 
times  without  any  apparent  change  of  position.  Generally,  however, 
not  more  than  two  eggs  were  placed  contiguously,  and  in  the  majority 
of  cases  they  were  placed  singly.  This  particular  female  laid  22  eggs 
that  were  observed.  The  eggs  are  viscid  externally  at  first,  but  they 
quickly  dry  and  remain  glued  in  position.  The  position  sought  by  the 
female  for  placing  the  eggs,  e.  g.,  the  eyes  or  buds  of  the  potato,  presents 
a  satisfactory  place  of  concealment  for  them,  and  is  also  the  place  where 
the  epidermis  of  the  potato  is  more  easily  penetrated  by  the  young 
larvse  than  at  any  other  point. 

Larva. — On  hatching,  the  larva  is  1  mm.  long  and  of  a  transparent 
white  color,  with  the  head  and  thoracic  region  darker.     Its  minuteness 


Fig.  3.    Larva.    Hair  line  indicates  natural  size. 

renders  it  difficult  of  observation,  and  it  is  only  noticed  by  the  ordinary 
observer  after  its  second  or  third  molt.  At  this  stage  it  is  quite  notice- 
able, being  from  5  to  6  mm.  long.  The  head  is  characteristically  of  a 
dark  brown  color,  with  the  mouth  parts  well  developed.  The  first 
thoracic  segment  is  of  a  clouded  pink  ("old  rose';)  color,  colored  over 
dorsally  with  the  dark  mahogany-colored  cervical  shield.  The  second 
thoracic  segment  shows  the  clouded  pink  color  both  dorsally  and  ven- 
trally,  and  the  third  thoracic  segment  is  clouded  white,  as  are  the  seven 
following  abdominal  segments.  This  clouded  white  color  may  verge  to 
yellow  and  to  green;  this  color-change  being  dependent  on  whether  the 
larva  has  been  feeding  on  the  heart  of  the  potato  or  on  greener  material 
near  the  surface.  Frequently  these  abdominal  segments  will  be  suf- 
fused dorsally  with  pink.  The  eighth  (terminal)  abdominal  segment 
is  of  a  shining  yellow  color.  The  various  segments  are  ornamented 
with  sparsely  scattered  hairs  or  spines. 

The  position  and  appearance  of  the  thoracic  as  well  as  of  the  abdomi- 
nal legs  are  shown  in  Fig.  3. 


—  11  — 


The  Chrysalis  and  Pupation. — The  chrysalis  is  6  mm.  long,  and  is  at 
first  a  light  yellow,  turning  very  soon  to  a  rich  mahogany  and  finally 
to  a  dark  mahogany  color.  The  ab- 
dominal segments  are  conspicuous, 
and  to  a  late  stage  in  the  chrysalis's 
life  are  quite  free  in  movement. 
The  wing-folds  are  free  from  the 
abdomen  distally;  the  ventrally- 
placed  antenna?  are  quite  well  defined; 
the  eyes  prominent.  Fig.  4  is  a  good 
representation  of  the  chrysalis. 

The  pupation  of  the  insect  is  inter- 
esting, and  can  be  observed  satis- 
factorily. The  larva  at  about  six 
weeks  age  comes  to  the  surface  and 
either  pupates  in  the  mouth  of  its 
burrow  after  it  has  broken  through 
the  epidermis,  or  seeks  some  depres- 
sion on  the  potato,  or  may  find  its 
way  into  some  crack  or  cranny  of  the 
receptacle  in  which  the  potatoes  are  stored.  It  has  been  frequently 
observed,  during  this  investigation,  to  find  its  way  into  the  fold  of  the 
sack  in  which  the  potatoes  are   kept.     Generally  speaking,  then,   the 


Fig.  4.    Chrysalis. 


Pupa  case  closed. 


Fig.  5. 


Pupa  case  open. 


worm  finds  a  more  or  less  secluded  place  and  there  pupates.  The 
satisfactory  spot  having  been  chosen,  it  proceeds  to  spin  its  silken 
cocoon   therein.      A    carpet   piece    of    silk    is    well    fastened    to    the 


—  12  — 

surface,  the  cover  piece  being  woven  at  the  same  time,  the  two 
together  forming  a  sort  of  pocket,  smooth  and  white  on  the  inner  side, 
but  on  the  outer  side  covered  with  bits  of  frass,  trash,  etc.,  and  assum- 
ing the  appearance  of  a  piece  of  dirt  and  nothing  more.  When  this 
covering  is  arranged  satisfactorily  externally  the  worm  gets  beneath 
it  and  sews  together  the  opening  remaining  at  the  end  of  the  pocket, 
and  transforms  to  the  chrysalis  in  safety  within  it. 

Fig.  5  shows  a  pupa  case  placed  within  a  very  slight  depression  to  con- 
ceal it,  and  also  the  same  pupa  case  with  the  cover  torn  loose  and 
turned  back  and  the  chrysalis  in  sight;  while  Fig.  6  shows,  at  the  end 


,■  .''.,;&■:'•   .,..;■■;.: 

/ 

!     M 

-■$Wr:.  *^Cr 

JF 

* 

Fig.  6.    Pupa  case  in  wound  caused  by  Stenopelmatus. 

of  the  pin,  a  pupa  case,  with  the  chrysalis  exposed,  in  a  wound  in 
the  potato  caused  by  the  yellow  ground  cricket  (Stenopelmatus  Sp., 
fig.  10).  The  pupa  cases  are  generally  so  cunningly  concealed  beneath 
their  bits  of  dirt  and  trash  that  they  may  easily  pass  unnoticed,  but 
they  are  quite  pervious  to  air  and  are  easily  destroyed.  (See  Remedies, 
p.  27.) 

LIFE  HISTORY. 

A  series  of  observations  covering  the  life  of  the  insect  for  nearly 
eleven  months  was  taken.  Two  lots  of  moths  were  studied  concur- 
rently, and  the  results  seemed  to  agree  in  the  main  points.  A  lot  of 
young  potato  plants,  stalks  and  leaves,  with  very  small  potatoes,  was 
obtained  and  kept  in  a  gauze-covered  case.  The  stalks  were  much 
infested  with  the  larvae,  and  as  these  stalks  wilted  the  larva?  worked  their 
way  out  of  them  and  across  the  intervening  space  of  10  cm.  (4  ins.)  and 
into  the  small  tubers.  They  continued  to  work  here  until  ready  to 
pupate,  and  then  came  to  the  surface  and  placed  their  chrysalides  in 
depressions  on  the  potato.  The  age  of  the  larvae  in  the  stalks  was  not 
known,  but  the  first  to  pupate  tunneled  out  of  the  potato  on  the  fifth 
day  after  entering,  and  in  eight  days  all  had  pupated.     On  the  thirteenth 


—  13  — 

day  after  pupation  the  first  moth  emerged,  and  on  the  sixteenth  day 
all  had  emerged.  This  gives  the  period  of  pupation  in  this  generation 
as  from  thirteen  to  sixteen  days.  The  adult  moths  can  carry  on  the 
life  functions  without  eating,  and  hence  breeding  in  storage  is  quite  easy. 

The  moths  mated  soon  after  emerging,  and  oviposition  was  noted  on 
the  second  day  after  emergence.  The  first  larvae  noted  were  recognized 
eight  days  after  oviposition,  and  new  larvae  appeared  on  the  two  follow- 
ing days.  These  young  larvae  were  carefully  observed,  and  forty-two 
days  later  they  began  to  come  out  of  the  potato  and  to  pupate,  and 
continued  to  appear  for  three  days  thereafter. 

The  second  lot  of  moths  was  carried  much  further  than  this  lot,  and 
their  history  is  as  follows:  A  lot  of  infested  potatoes  was  purchased 
from  a  dealer,  and  on  September  17,  1900,  nine  moths  were  taken  from 
this  lot  and  placed  with  some  uninfested  potatoes ;  on  the  18th,  the 
copulation  of  two  pairs  was  noted;  on  the  20th,  three  females  were 
noted  ovipositing  (see  Oviposition,  p.  9).  On  September  28th  three 
larvae  were  noted;  on  the  29th  six  larvae,  and  on  the  30th  five  larvae. 
On  November  12th  two  larvae  came  to  the  surface  and  made  cocoons  ; 
on  the  13th  six  larvae  went  into  this  condition ;  on  the  14th  twelve 
more,  and  on  the  15th  six  more.  On  November  28th  three  moths 
emerged,  on  the  29th  seven  moths,  on  the  30th  eight  moths,  on  Decem- 
ber 1st  seven  moths,  and  on  December  2d  one  moth.  On  December  2d 
a  number  of  moths  from  this  generation  were  placed  in  breeding  cages 
with  uninfested  potatoes,  and  on  December  3d  oviposition  was  noted. 
On  December  10th  larvae  were  recognized,  and  these  larvae  began  to  spin 
up  on  January  21,  1901,  and  by  January  23d  eighteen  cocoons  were 
noted.  On  February  7th  the  moths  had  begun  to  emerge,  and  on  Febru- 
ary 8th  fourteen  adults  were  noted.  This  gave  about  the  same  time  for 
this  generation  to  complete  its  cycle  as  in  the  previous  case. 

The  same  process  of  placing  the  moths  with  uninfested  potatoes  was 
repeated  and  the  same  results  obtained,  save  in  the  case  of  the  larvae, 
where  the  life  period  was  extended  to  nine  weeks  (a  sort  of  hibernation?), 
and  adult  moths  appeared  on  the  4th  day  of  May,  1901.  Again  was 
the  process  repeated,  and  a  new  lot  of  moths  appeared  on  the  9th  of 
July,  when  the  breeding  was  abandoned. 

We  may  summarize  the  life  history  thus:  To  complete  the  cycle 
ordinarily,  63  to  69  days  are  needed,  save  for  the  winter  generation 
when  this  time  may  be  extended  to  84  or  85  days ;  this,  of  course,  under 
the  temperature  conditions  of  Berkeley.  This  time  is  divided  thus:  Egg 
stage,  7  to  10  days  ;  larvae,  42  to  45  days  ordinarily,  winter  generation 
9  weeks  ;  chrysalis,  14  to  16  days;  adult  life,  indefinite  but  short. 

This  study  of  the  life  of  the  insect  is  significant  from  the  fact  that  the 
conditions  for  living  and  propagating  were  the  same  as  are  found  when 
potatoes  are  stored,  and  the  result  indicates  conclusively  that  the  injury 


—  14  — 

is  progressive.  A  very  small  primary  infestation  may  in  a  few  weeks 
mean  the  complete  ruin  of  the  infested  lot.  Also,  it  is  to  be  noted  that 
the  adult  moth  is  ready  for  the  young  potato  plants  as  soon  as  they 
appear  in  the  spring.  Under  storage  conditions  the  generations  will 
not  be  so  clearly  defined  as  in  the  laboratory  conditions,  and  there  will 
be  an  apparent  lapping-over  of  broods,  and  adults  will  be  noted  at  all 
times.  This  "lapping-over"  of  course  results  in  the  adult  being  ready 
to  do  damage  at  almost  any  time  that  material  is  presented  for  it  to 
work  upon.  The  necessity  is  obvious,  therefore,  of  destroying  the  moth 
in  infested  storerooms,  bins,  etc.,  and  not  permitting  it  to  escape  and 
spread  the  infection.  This  aspect  of  the  case  will  be  treated  of  more 
fully  under  the  heading  of  "  Remedies." 

CHARACTER    OF    INJURY. 

The  injury  done  by  the  insect  naturally  falls  under  two  heads:  the 
injury  to  the  growing  plant  and  the  injury  to  the  tubers.  The  character 
of  the  injury  in  the  first  case,  that  of  to  the  plant,  has  been  touched  on 

on  page  5,  and  is  perhaps  not 
so  often  noted  as  is  the  injury 
to  the  tubers.  When  the  moth 
oviposits  on  the  plant  she  seeks 
some  desirable  position,  such 
as  the  base  of  a  leaf,  in  which 
to  place  the  egg,  and  the  young 
larva  on  hatching  immediately 
burrows  beneath  the  epidermis 
of  the  plant  and  eats  its  way 
along  downward,  always  just 
beneath  the  epidermis.  This 
fig.  7.  sub-epidermal  burrow.  burrow    can    be    quite    easily 

traced  when  the  larva  begins 
to  attain  some  size,  and  by  careful  search  can  be  detected  even  when 
the  larva  is  quite  young.  The  worm  fills  the  burrow  behind  itself  with 
excrement,  and  this  ejected  material  turns  quite  dark  in  color.  Follow- 
ing in  the  wake  of  this  primary  injury  is  the  inevitable  mould  and 
fungous  growth,  and  the  stalk  soon  succumbs  to  the  combined  injuries, 
the  actual  material  taken  as  food  by  the  worm  and  the  consequent  decay. 
The  injury  to  the  tuber  is  very  similar  to  that  to  the  plant.  The 
worm  enters  the  potato  and  burrows  its  way  through  the  tissue  of  the 
tuber.  This  entry  is  in  the  bud,  and  the  point  of  entry  is  generally 
marked  by  a  little  pile  of  excrement.  The  worm  having  succeeded  in 
entering,  tunnels  along  beneath  the  epidermis  or  right  through  the 
substance  of  the  potato.  It  does  not  seem  to  be  at  all  particular  which 
method  it  follows,  and  indeed  may  show  both  kinds  of  work.     When 


—  15  — 

the  burrow  is  sub-epidermal  it  may  be  easily  traced  by  the  shrinkage  of 
the  potato  on  either  side  of  it,  as  is  shown  in  Fig.  7.  When  the 
burrow  is  in  the  substance  of  the  potato  it  is  very  evident  and  can  be 
easily  traced  by  the  discolored  excrement.  The  frontispiece  illustrates 
both  kinds  of  work.  The  potato  has  been  cut  in  such  a  way  as  to 
show  both  a  sub-epidermal  burrow  and  also  certain  burrows  into  the 
body  of  the  potato.  These  burrows  are  rilled  with  excrement,  and 
render  the  potato  wholly  unfit  for  human  food.  The  burrows,  with 
their  excremental  filling,  soon  become  the  starting  points  for  rots  and 
fungous  diseases,  as  previously  noted  (p.  5),  and  the  injury  is  complete. 

MODES   OF   INFECTION. 

There  are  various  ways  in  which  the  potatoes  may  become  infected, 
and  these  ways  may  be  described  in  this  order: 

By  infection  of  the  stem:  The  adult  female  moth,  being  on  the  wing 
when  the  young  potato  plant  appears  above  the  ground,  oviposits  on 
the  plant  itself  at  a  point  near  the  junction  of  a  leaf  with  the  stem. 
The  larva  hatches  and  immediately  begins  work  by  "mining"  a  burrow 
beneath  the  epidermis.  The  general  trend  of  this  burrow  is  downward, 
though  a  spiral  course  may  be  pursued.  If  the  attack  has  been  made 
on  a  very  young  plant  the  larva  may  come  to  maturity  and  work  its 
way  out  of  the  stem  and  pupate  in  the  ground  beside  the  plant  or  in 
some  depression  in  the  stalk  itself.  In  this  case  the  tuber  is  not 
injured,  but  the  plant  suffers  both  because  the  nutriment  has  been 
taken  from  it  and  also  because  of  bacterial  and  fungous  diseases  bred 
in  the  excrement  with  which  the  burrow  is  filled.  Cases  have  been 
reported  to  us  where  hundreds  of  acres  of  potatoes  have  been  wholly 
lost  through  an  attack  of  this  kind.  If  the  oviposition  takes  place  in 
an  older  plant,  the  larva  burrows  down  the  stalk  as  before,  but  the 
hardening  of  the  plant  causes  it  to  leave  and  enter  a  tuber  and 
continue  operations  there.  This  entry  is  generally  made  near  a  bud  or 
eye,  and  the  larva  actually  passes  out  of  the  stem  and  through  the 
surrounding  earth  to  the  tuber,  and  not  down  the  stem  and  into  the 
tuber,  as  is  generally  stated.  On  infested  plants  observed  in  the  labora- 
tory the  larva  left  the  stalk  and  crossed  over  the  space  of  one  deci- 
meter (4  inches)  of  earth  to  potatoes  placed  at  this  distance  from  them. 
When  the  larva  had  found  the  potato  it  would  wander  about  the  sur- 
face for  some  time,  twenty-four  hours  in  some  instances,  but  seemed  to 
have  no  difficulty  in  finally  piercing  the  skin  and  entering. 

By  direct  infection  of  the  tuber  in  the  hill:  In  the  experimental  plot 
it  was  noted  that  in  many  cases  there  were  tubers  that  were  not  com- 
pletely covered  in  the  "  hilling  "  process.     The  exposed  portions  of  these 


—  16  — 

tubers,  being  open  to  the  light,  turned  green,  and  the  moth  oviposited  in 
these  green  places.  The  fact  that  the  fully  covered  tubers  in  the  same 
hill  were  entirely  free  from  the  larvae,  and  the  further  fact  that  in  some 
cases  remnants  of  the  egg  were  found  in  these  green  places  on  the 
potatoes,  shows  the  direct  infection  in  the  hill. 

Direct  infection  after  digging:  The  moth  will  oviposit  in  the  potatoes 
that  are  left  exposed  in  the  field  after  digging.  Many  perfectly  clear 
tubers  were  so  exposed,  and  in  the  large  majority  of  cases  these  tubers 
were  later  found  infested;  in  one  case  five  larvae  were  taken  from  one 
potato. 

Indirect  infection  after  digging:  If  the  stems  are  infested  at  the 
time  of  digging,  the  larvae  will  leave  them  and  find  their  way  to  and 
enter  the  tubers,  if  these  are  available.  The  common  practice  in  the 
potato  fields  of  covering  the  piles  of  newly  dug  tubers  with  the  leaves 
and  stems  of  the  plants  by  way  of  shade  is  a  sure  way  to  secure  infesta- 
tion if  the  latter  contain  larvae.  Even  though  the  leaves  and  stems 
may  be  uninfested  the  practice  of  using  them  as  a  covering  is  not  to  be 
commended,  as  when  they  are  used  for  this  purpose  they  also  furnish  a 
place  of  concealment  for  the  moth  in  close  proximity  to  the  tubers. 

Infection  in  the  sack  or  bin:  The  moth  will  oviposit  on  the  stored 
potatoes.  A  number  of  clear  tubers  were  placed  in  a  gauze-covered  box, 
and  a  lot  of  the  moths  placed  with  them.  Infestation  always  followed 
this  experiment. 


EXPERIMENTS    IN    FIELD    OR    STOREROOM. 

The  experiments  here  detailed  were  carried  on  with  the  surrounding 
conditions  made  to  conform  as  nearly  as  possible  to  the  natural  con- 
ditions. The  field  work  in  all  its  aspects  was  a  duplicate  of  the  ordinary 
farm  conditions,  and  the  laboratory  work  might  well  pass  for  a  series  of 
experiments  carried  on  in  storerooms.  It  is  believed  that  the  field 
results  obtained  can  be  obtained  in  regular  farm  practice,  and  that  any 
one  storing  potatoes  can  duplicate  the  results  obtained  in  the  laboratory. 
As  a  matter  of  course,  great  care  was  exercised,  not  alone  in  carrying  on 
the  experiments,  but  so  far  as  possible  this  was  done  with  a  view  to  the 
expense  account,  and  no  work  requiring  a  heavy  outlay  was  attempted, 
nor  would  such  be  required  in  commercial  practice.  Infested  potatoes  were 
purchased  in  the  open  market  and  used  for  laboratory  experiments,  as 
well  as  the  product  of  a  patch  of  sound  potatoes  planted  on  the  Station 
grounds.  This  patch  and  its  product  served  as  a  basis  for  much  of  the 
field  observation  and  experiment,  and  this  work  at  the  Station  was  sup- 
plemented by  studies  made  in  large  fields  of  infested  potatoes  and  by 
observation  and  inquiry  in  the  warehouses  and    storerooms  of  many 


—  17  — 

dealers.  Whenever  cases  were  reported  that  appeared  to  present  features 
of  value  in  this  inquiry  no  pains  have  been  spared  in  investigating  them, 
and  as  a  result  we  are  able  to  present  a  fairly  complete  account  of  the 
insect  and  its  work  in  California,  which  knowledge,  if  applied  in  hand- 
ling potatoes,  should  cause  a  marked  diminution  in  the  loss  from  the 
work  of  the  insect. 

Field  Experiments. — On  March  7,  1901,  the  experimental  patch  of 
potatoes  was  planted  on  the  Station  grounds  in  Berkeley.  The  soil  is  a 
medium  heavy  loam,  and  was  well  plowed.  The  seed-potatoes  used 
were  Oregon  Burbanks,  and  were  perfectly  clear  of  infestation.  The 
season  was  rather  cool,  and  the  potatoes  did  not  appear  above  ground 
until  April  1st.  By  the  end  of  April  the  plants  were  growing  well  and 
were  quite  thrifty.  Scarcely  any  plant-infestation  was  noted  up  to  this 
date,  though  to  insure,  if  possible,  such  infection  a  number  of  moths, 
bred  in  confinement,  were  liberated  in  the  patch  on  April  5th.  Whether 
these  were  the  moths  that  were  instrumental  in  infecting  the  plants  is 
of  course  open  to  question;  however,  on  April  25th  six  affected  plants 
were  noted,  and  on  two  of  these  remnants  of  the  eggs  were  found.  The 
affected  stalks  were  cut  off  and  destroyed  in  these  six  cases,  and  the 
result  was  a  complete  stoppage  of  the  trouble  with  these  plants.  The 
plants  seemed  to  suffer  in  nowise  from  this  lopping-off  process,  and 
when  these  hills  were  dug  it  was  found  that  the  yield  was  up  to  the 
average  of  surrounding  hills.  It  must  not  be  understood  that  the  whole 
head  was  removed  in  these  six  cases — only  the  affected  stalks  were  cut 
off  just  below  where  the  trouble  was  manifest.  On  the  night  of  April 
25th,  after  the  affected  stalks  had  been  noted,  an  experiment  was  tried 
with  a  crude  lantern  trap,  and  in  one  hour  fourteen  of  the  moths  were 
taken  at  one  candle.  The  trap  was  merely  a  small  sheet  of  bright  tin 
used  as  a  reflector,  and  a  candle  set  up  in  a  basin  of  water  on  which  a 
little  kerosene  oil  was  floating.  This  trap  was  tried  subsequently  a 
number  of  times,  and  demonstrated  beyond  a  doubt  that  the  moth  can 
be  destroyed  in  large  numbers  by  the  use  of  light-traps.  It  is  interest- 
ing to  note  in  this  connection  that  more  potato  moths  than  of  all  other 
species  combined  were  taken,  and  that  the  majority  (60%)  of  the  potato 
moths  taken  at  this  trap  were  females;  and  since  one  female  lays  many 
eggs  and  can  infect  many  plants,  the  value  of  this  method  of  destruction 
is  evident.  It  was  not  desired  to  reduce  the  moths  to  below  the  danger 
limit  on  this  patch,  so  the  light-experiments  were  at  no  time  carried  on 
for  more  than  an  hour.  The  moths  taken  at  the  light  certainly  came 
from  the  surrounding  locality,  the  date  of  capture  as  well  as  their 
numbers  precluding  the  possibility  of  their  being  those  originally  turned 
loose  in  the  patch,  and  it  was  also  too  soon  for  their  progeny. 

2— Bul.  135 


—  18  — 

As  the  worm,  on  hatching,  at  once  burrows  into  and  feeds  upon  the 
tissue  of  the  plant,  and  as  the  egg  is  laid  where  it  is  difficult  to  reach 
with  sprays,  no  experiments  along  this  line  were  made. 

The  next  field  experiments  tried  were  when  the  potatoes  began  to 
form  and  the  time  of  hilling  arrived.  The  earth  about  a  number  of 
plants  was  well  pulverized,  and  this  specially  pulverized  earth  used  to 
hill  with.  The  result  was  a  good,  compact  hill,  with  the  potatoes  well 
covered  and  difficult  for  the  moth  or  worm  to  get  to.  Vyhen  the  potatoes 
were  dug  from  these  hills  no  infestation  was  found  in  them,  though 
the  check  hills  on  either  side  were  infested.  These  check  hills  were 
"hilled"  in  the  ordinary  way,  and  the  earth  here  being  quite  cloddy 
certain  of  the  potatoes  were  somewhat  exposed.  In  every  case  of  such 
exposure  it  was  found  that  the  potato  was  infested.  In  certain  of  the 
hills  the  earth  was  scraped  away  so  as  to  expose  one  or  more  of  the 
potatoes  to  the  light.  The  exposed  parts  of  the  potatoes  turned  green 
and  it  was  found  in  every  case  that  these  potatoes  were  infested  and  that 
the  work  of  the  worm  began  in  this  green  part.  Likewise,  taking  the 
whole  field  when  the  potatoes  were  finally  dug,  it  was  found  that  95 
per  cent  of  the  ones  showing  green  places  were  infested,  and  that  the 
infestation  in  every  case  began  in  these  green  places.  Furthermore,  in 
all  cases  where  potato  fields  were  found  infested  it  was  noted  that  this 
rule  held — that  the  soil  was  either  lumpy  and  the  potatoes  exposed 
more  or  less,  or  was  fine  and  dry,  quite  sandy  for  instance,  but  not  com- 
pact.    In  either  case  the  potatoes  were  easy  to  reach. 

Again,  it  has  been  noted  in  the  course  of  this  investigation  that  right 
in  the  midst  of  affected  fields  a  field  will  be  found  in  which  the  tubers 
are  not  affected,  and  invariably  the  reason  of  this  non -infestation  has 
been  found  to  be  the  careful  hilling  of  the  plants.  It  has  further  been 
noted  that  a  rain  coming  after  hilling,  as  occasionally  happens,  has  a 
tendency  to  compact  the  earth,  and  the  potatoes  which  were  covered  in 
these  compacted  hills  were  unaffected.  Indeed,  all  the  experimental 
work  and  all  the  field  observations  point  to  the  fact  that  careful  com- 
pact hilling  reduces  the  infection  to  a  minimum,  and  too  much  emphasis 
cannot  be  put  upon  this  phase  of  farm  practice. 

Finding  that  the  potatoes  exposed  in  the  hills  were  almost  invariably 
infested  led  to  a  series  of  experiments  on  the  question  of  exposure.  It 
was  noted  that  in  ordinary  farm  practice  the  potatoes  are  frequently  left 
exposed  for  varying  times  when  digging  was  in  progress,  and  a  number 
of  potatoes  known  to  be  uninfested  were  left  exposed  in  the  field  for 
times  varying  from  two  to  ten  hours  in  daylight.  The  following  table 
gives  the  results  of  this  experiment: 


19 


Table  Showing  Results  of  Exposure  Experiments. 


Lot. 

Number  of 
Potatoes. 

Time  of  Exposure. 

Hours 
Exposed. 

Number 
Infected. 

Percentage  of 
Infestation. 

A 

40 

8  A.  M.  tO  10  A.  M. 

2 

1 

2.5 

B 

40 

8  A.  M.  tO  12  M. 

4 

4 

10.0 

C 

40 

8  A.  M.  tO     2  P.  M. 

6 

9 

22.5 

D 

40 

8  A.  M.  tO     4  P.  M. 

8 

17 

42.5 

E 

40 

8  A.  M.  tO     6  P.  M. 

10 

29 

72.5 

It  will  be  seen  from  this  table  that  a  very  small  percentage  of  those 
potatoes  which  were  exposed  for  the  shortest  time,  two  hours,  were 
infected,  and  the  increase  in  infection  shown  in  the  second  lot,  B, 
where  the  exposure  was  two  hours  longer,  is  not  large.  The  rise  in  per 
cent  of  infection  shown  in  lots  C,  D,  and  E  is  significant,  indicating, 
as  it  does,  not  only  the  danger  of  long  exposure,  but  also  the  rapid  rise 
in  infection  in  the  latter  part  of  the  day.  The  results  show  that 
exposure  of  the  tubers  should  always  be  avoided,  and  that  special  care 
should  be  taken  not  to  expose  them  in  the  late  afternoon. 

Another  experiment  tried  in  this  matter  of  exposure  was  to  leave  a 
lot  of  forty  potatoes  out  in  the  field  from  six  o'clock  in  the  evening 
until  eight  o'clock  the  next  morning.  The  result  was  that  all  of  the 
potatoes  were  infected,  showing  the  extreme  danger  in  leaving  the  potatoes 
exposed  in  the  field  over-night. 

Another  series  of  experiments  was  based  on  the  fact  that  it  had  been 
found  in  the  laboratory  that  the  worms  would  leave  infested  stalks 
when  they  began  to  wither,  and  enter  the  tubers.  When  the  potatoes 
were  dug,  a  number  of  tubers  known  to  be  uninfested  were  stacked  in 
the  field  and  covered  with  the  infested  stalks,  and  this  pile  was  in  turn 
closely  covered  with  cloth,  so  that  no  direct  infection  by  the  moth 
could  occur.  As  a  check  to  this  experiment  an  equal  number  of  unin- 
fested potatoes  were  stacked  in  the  field,  but  no  stalks  were  piled  upon 
them.  This  stack,  too,  was  closely  covered  with  cloth..  Of  the  pota- 
toes covered  with  the  stalks  70  per  cent  were  finally  found  to  be  infested 
with  the  worm,  while  of  those  not  covered  with  stalks  none  were  infected. 
Now,  it  is  a  common  practice  in  the  potato  fields  to  cover  the  newly- 
dug  tubers  with  the  stalks,  and  if  these  stalks  are  infested  the  tubers 
are  sure  to  suffer.  Furthermore,  even  were  the  stalks  uninfested  the 
practice  of  covering  the  tubers  with  them  is  highly  undesirable,  as  a 
good  shelter  for  the  moth  is  thus  formed.  Observations  in  the  field 
show  that  the  moth  is  particularly  abundant  in  piles  of  the  stalks,  and 
it  may  be  expected  that,  taking  advantage  of  this  shelter  if  it  is  present 
in  the  field,  it  will  lay  its  eggs  on  the  tubers  below. 


—  20  — 

A  series  of  experiments  was  tried  on  plants  with  infested  stalks,  the 
infection  occurring  in  this  case  when  the  plants  were  quite  old.  The 
experiments  were  suggested  by  the  fact  that  as  the  plant  begins  to  ripen 
and  harden  the  worms  leave  the  stalks  and  seek  the  more  succulent 
food  found  in  the  tubers  in  the  ground.  The  plants  selected  for  these 
experiments  were  watched  quite  closely,  and  one  week  before  time  of 
digging  the  heads  were  cut  off  just  beneath  the  ground.  These  heads,  with 
the  larvse  still  in  them,  were  removed  and  destroyed.  When  these  hills 
were  dug  the  potatoes  were  found  to  be  uninfested,  though  the  check 
hills  with  worms  in  the  stalks  were  infested,  the  worms  having  left  the 
stalks  and  entered  the  tubers.  It  was  also  found  that  the  potatoes  in 
these  decapitated  hills  were,  if  anything,  better  and  larger  than  those  in 
the  check  hills  in  which  the  heads  remained  undisturbed. 

We  have,  in  this  matter  of  removing  and  destroying  infested  heads,  a 
very  promising  means  of  defense  against  the  moth,  and  one  that  is  easily 
used  in  field  practice.  The  cheapest  and  at  the  same  time  the  most 
satisfactory  way  of  removing  the  heads  has  been  found  to  be  by  the  use 
of  a  knife.  The  method  of  procedure  is  for  a  man  to  walk  along  a 
row,  and  when  an  infested  plant  is  found  by  him  to  cut  it  off  just 
beneath  the  surface  of  the  ground.  With  a  little  practice  the  infested 
plants  will  be  easily  recognized  from  their  somewhat  wilted  appearance. 
Other  men  follow  the  cutters,  gathering  up  and  removing  the  stalks 
from  the  field.  These  stalks  should  be  placed  in  piles  and  covered  with 
a  few  inches  of  earth,  and  fermentation  and  heating  soon  following,  the 
larvae  are  destroyed.  The  piles  of  decayed  vegetable  matter  may  be 
spread  over  the  field  and  plowed-in,  thus  enriching  the  soil. 

All  of  the  experimental  work  in  the  field  indicated  the  necessity  of 
avoiding  exposure  of  the  potatoes  as  completely  as  possible,  and  where 
this  non-exposure  policy  was  fully  carried  out  it  was  found  to  eliminate 
entirely  this  source  of  infection. 

The  conclusions  arrived  at  in  the  work  outlined  above  were  confirmed 
by  the  results  obtained  in  another  plot  of  potatoes  planted  on  the  Station 
grounds,  but  for  purposes  other  than  the  study  of  the  potato-worm. 
This  plot  was  also  seeded  with  Oregon  Burbanks,  and  the  work  done 
upon  it  was  exactly  that  which  prevails  in  ordinary  farm  practice.  No 
particular  care  was  taken  in  hilling,  and  exposure  at  digging  was  not  in 
any  way  guarded  against.  The  yield  of  this  plot  was  practically  worth- 
less, 75  per  cent  of  the  potatoes  being  wormy,  and  yet  the  original  danger 
of  infection  was  no  greater  than  in  the  case  of  the  experimental  plot. 

The  results  obtained  from  these  exposure  experiments  led  us  to  another 
series  of  investigations.  It  was  noted  that  the  moth  was  almost  sure 
to  find  the  potatoes  if  they  were  in  the  field,  and  the  question  arose 
whether  they  would  winter  in  potatoes  left  in  the  field.  To  decide  this 
question  a  number  of  infested  tubers  were  left  out  of  doors  in  gauze- 


—  21  — 

covered  receptacles,  but  exposed  to  all  weather  conditions  occurring 
through  the  winter.  Many  of  these  potatoes  rotted  completely  before 
the  winter  passed,  but  some  of  them  remained  in  sound  enough  con- 
dition to  carry  the  insects  through  the  winter,  and  far  enough  into  the 
spring  for  the  young  potato  plants  to  be  sufficiently  grown  to  furnish  a 
feeding-place  for  the  larvae.  This  would  indicate  that  if  waste  potatoes 
were  left  in  the  field  after  digging,  the  moth  would  be  carried  over  the 
rainy  season  in  them,  and  this  is  just  what  seems  to  have  happened  in 
the  following  case.  In  the  course  of  this  investigation  an  isolated  field  of 
potatoes  three  acres  in  extent  was  found  to  be  badly  infested  with  worms, 
so  badly,  indeed,  that  the  tubers  were  wholly  unsalable.  The  field  is 
owned  and  worked  by  a  gentleman  who  runs  a  country  store  in  a  near-by 
village,  and  its  history  was  obtained  from  him.  In  1899,  the  crop  was 
good  and  not  wormy.  In  1900,  some  worms  in  the  potatoes  and  some 
complaint  from  buyers.  In  1901,  potatoes  so  wormy  as  to  be  unsalable. 
Methods  of  planting,  cultivation,  etc.,  the  same  each  year.  Soil  a  sandy 
loam,  well  drained.  Small  and  waste  potatoes  and  tops  always  left  on 
the  ground  and  plowed-in.  An  investigation  of  the  neighborhood  dis- 
closed a  small  amount  of  " night  shade"  {Solarium  nigrum),  but  hardly 
enough  to  more  than  account  for  the  original  infection.  There  was 
always  a  number  of  potatoes  on  the  ground  when  seeding  began.  The 
progressive  infestation  noted  in  this  field,  which  is  an  example  of  many 
fields,  was  evidently  due  to  this  item  of  bad  farm  practice,  viz.,  leaving 
the  waste  product  on  the  ground. 

As  a  corollary  to  the  results  noted  in  this  case,  care  should  be  taken 
never  to  use  infested  seed  potatoes,  as  the  moth  is  more  than  likely  to 
come  out  from  them  in  force,  in  time  to  infect  the  young  plants;  and, 
besides,  the  best  farm  practice  is  to  use  the  largest  and  most  vigorous 
potatoes  as  seed.  In  infested  potatoes  the  worm  has  taken  so  much  of 
the  substance  and  thus  robbed  the  young  plant  of  so  much  of  the  stored 
nutriment  that  it  will  be  correspondingly  weak,  and  will  to  this  extent 
more  quickly  succumb  to  the  attack  of  the  worm.  It  is  also  generally 
conceded  that  in  an  insect  attack  the  less  vigorous  the  plant  the  more 
likelihood  that  the  insect  will  choose  it  to  work  upon. 

Storage  Experiments. — The  experiments  carried  on  with  stored  potatoes 
were  intended,  first,  to  determine  the  life  history  of  the  insect  (see  p.  12) ; 
second,  to  discover  whether  the  life  of  the  pest  could  be  continued 
through  several  generations  or  indefinitely  without  the  adult  having 
access  to  food;  and  finally,  to  determine  what  means  could  be  used  most 
practically  to  stop  the  infection  in  the  potatoes  if  it  were  found  that 
breeding  did  take  place  freely  among  the  stored  tubers.  To  initiate 
these  experiments  infested  potatoes  were  obtained  and  placed  in  gauze- 
covered  receptacles,  and  the  emergence  of  the  moths  noted.     When  the 


—  22  — 

moths  were  quite  numerous  in  these  receptacles  fresh  potatoes  that 
were  known  to  be  uninfested  were  introduced.  These  potatoes  were 
marked  so  that  they  could  be  easily  identified  at  any  time,  and  sooner 
or  later  they  were  always  found  to  be  infested,  thus  proving  that  the 
moths  could  and  did  breed  in  storage,  and  that  the  damage  from  them 
was  continuous  and  progressive.  The  study  of  the  life  of  the  insect 
(see  p.  12),  carried  on  as  it  was  from  the  end  of  one  growing  season  to 
the  end  of  another,  eleven  months  later,  proved  that  this  breeding  in 
storage  could  extend  over  several  generations — four,  as  noted  in  this 
investigation.  This  continuance  of  the  moth  under  storage  conditions 
proved,  also,  how  numerous  the  progeny  of  a  single  pair  may  become  in 
a  few  months,  for  at  no  time  was  any  disease  noted  among  them,  nor 
was  any  parasitization  observed,  and  their  life  work  seemed  to  be  carried 
on  practically  unhindered. 

That  the  female  moth  may  lay  twenty-two  eggs  has  been  noted,  and 
considering  that  half  of  the  eggs  laid  will  produce  moths  of  the  same 
sex,  we  find  the  progeny  of  a  single  female  will,  if  food  is  present, 
number  at  the  end  of  six  months  some  15,000  moths  ready  to  oviposit 
upon  any  potato  plants  that  may  be  present. 

Of  course,  there  would  be  natural  checks  to  the  moth  when  its  life  is 
carried  on  out  of  doors  and  when  having  to  contend  with  unfavorable 
weather-conditions.  Two  of  the  breeding-cages  used  were  not  inter- 
fered with  at  all  from  the  first  of  November,  1900,  to  the  last  of  March, 
1901.  Ten  potatoes  were  in  each  of  these  cages,  and  when  they  were 
finally  abandoned  the  potatoes  had  sent  out  sickly  sprouts  and  these 
sprouts  had  been  killed  by  the  worms  working  in  them.  The  potatoes 
themselves  were  honeycombed  with  the  burrows  of  the  worms,  and  were 
so  shriveled  as  to  be  hardly  recognized  as  potatoes.  Some  of  them  had 
rotted,  but  by  maintaining  dry  conditions  as  far  as  possible  most  of 
them  had  escaped  decay.  The  dead  moths  in  these  cages  were  not 
counted,  but  they  were  numerous  enough  to  fill  a  half-pint  cup,  proving 
that  the  breeding  was  carried  on  in  confinement  under  loose  storage 
conditions. 

To  decide  whether  the  progressive  infestation  went  on  if  the  tubers 
were  packed  as  in  sacks,  two  ten-pound  lots  of  potatoes  were  put  up  in 
ordinary  jute  sacking.  One  of  these  lots  had  no  infestation,  while  in 
the  other  lot  several  infested  tubers  were  placed.  These  two  sacks  were 
put  close  together  in  a  gauze-covered  box,  and  left  for  three  months. 
On  examination  at  the  end  of  this  time  five  infested  tubers  were  found 
in  the  sack  that  was  originally  uninfested,  and  in  the  other,  the  origin- 
ally slightly  infested  sack,  hardly  a  good  uninfested  potato  was  found. 
That  the  infection  may  spread  in  sacked  potatoes  and  from  one  sack  of 
potatoes  to  another  in  the  same  pile  cannot  be  doubted. 


—  23  — 

Experiments  with  Carbon  Bisulfid. — It  having  been  conclusively  shown 
in  this  investigation  that  breeding  went  on  rapidly  in  the  stored 
potatoes,  methods  of  destroying  the  pest  were  sought  for — methods 
that  would  be  effective  even  when  the  potatoes  were  piled  "  heavy  "  in  the 
storerooms.  We  believe  that  there  is  no  way  of  reaching  the  worm 
when  it  is  once  in  the  potato,  except  the  destruction  of  the  potato  itself. 
A  potato  that  is  wormy  may  be  looked  upon  as  hopeless,  and  should 
be  rendered  harmless  in  the  spreading  of  infection,  by  being  boiled  and 
fed  to  hogs  or  destroyed  in  some  other  way.  But  it  is  impossible  in  the 
generality  of  cases  to  destroy  or  even  find  these  infested  potatoes  before 
they  have  spread  the  infection,  and  so  the  question  reduces  itself  to 
stopping  the  latter  without  attempting  to  find  and  destroy  the  individual 
tubers  that  are  affected.  Both  the  pupae  and  the  newly-emerged  moth 
are  easily  killed,  and  it  was  considered  that  in  these  stages  the 
vulnerable  point  was  to  be  found. 

Numerous  experiments  were  made  to  test  the  susceptibility  of  the 
chrysalis  to  the  fumes  of  carbon  bisulfid  (CS2),  and  these  proved  that 
we  have  in  this  substance  the  means  of  controlling  the  insect,  so  far  as 
the  infestation  in  stored  potatoes  is  concerned.  These  experiments  were 
made  in  the  following  manner:  Potatoes  were  taken  with  pupae  on  them 
of  all  ages,  from  those  which  had  just  spun  up  to  those  just  ready  to 
emerge.  These  potatoes  were  placed  in  a  tight  box  and  a  varying 
amount  of  carbon  bisulfid  put  in  a  shallow  dish  on  top  of  them,  and 
then  a  close  cover  put  on  the  box.  This  "bin"  was  allowed  to  stay 
closed  two  days,  and  then  the  potatoes  with  their  pupae  attached  were 
removed  to  the  gauze-covered  cases  and  closely  watched.  Every  chrysa- 
lis was  dead,  as  was  shown  by  no  moths  emerging,  though  the  observa- 
tions were  kept  up  for  eight  weeks. 

The  amount  of  carbon  bisulfid  used  in  this  and  the  following  experi- 
ments was  not  measured,  though  it  was  in  no  case  more  than  one  drachm 
to  the  cubic  foot  of  space,  and  the  amount  used  was  in  all  cases  more 
than  enough  to  kill  all  chrysalids.  The  amount  recommended  to  be 
used,  under  the  head  of  "  Remedies,"  is  based  on  the  calculations  made 
for  the  disinfection  of  grain  in  bins. 

These  experiments  were  followed  by  others,  in  which  the  life-history 
study  was  used  as  a  guide  for  the  time  to  apply  the  poison.  In  each 
experiment  there  were  used  a  number  of  infested  tubers  in  which  the 
worms  had  not  begun  to  make  their  cocoons.  It  was  supposed  that 
there  might  be  larvae  of  all  ages  in  these  potatoes,  and  also  possibly 
some  pupae  on  them,  so  the  tubers  were  treated  with  the  bisulfid  as  soon 
as  placed  in  the  "bin."  Two  weeks  later  the  potatoes  were  again 
treated  with  bisulfid,  and  this  was  repeated  twice  more  at  intervals  of 
two  weeks,  when  it  was  considered  that  probably  all  the  worms  had 


—  24  — 

spun  and  all  the  chrysalids  were  killed.  This  proved  to  be  the  case,  for 
the  infestation  in  this  lot  was  ended,  and  though  the  once  infested 
potatoes  finally  rotted,  this  did  not  occur  until  ample  time  had  elapsed 
for  the  moth  to  appear,  if  any  of  the  insects  had  remained  alive. 
Several  experiments  were  tried  in  this  line  with  a  less  number  of  treat- 
ments, and  while  some  were  successful  where  but  three  applications  of 
bisulfid  were  made,  this  reduction  of  the  number  of  applications  was 
not  always  a  success,  for  the  infestation  continued  in  some  cases. 

The  fact  before  noted,  that  under  ordinary  storage  conditions  there  is 
more  or  less  lapping-over  of  generations,  must  be  borne  in  mind,  and  if 
infestation  of  the  tubers  is  suspected  or  noted,  then  a  treatment  imme- 
diately on  their  being  placed  in  storage  is  imperative.  This  first  treatment 
kills  all  pupse  that  may  have  appeared  before  this  time.  The  second 
treatment  cares  for  all  the  chrysalids  that  may  appear  after  the  first 
treatment,  and  does  not  give  time  for  the  moth  to  emerge  from  them; 
the  third  treatment  disposes  of  the  pupse  that  may  appear  after  the 
second  treatment;  while  the  fourth  treatment  finishes  all  possible  late 
pupse.  This  is  under  the  supposition  that  potatoes  unexposed  to  the 
moth  after  digging,  are  being  dealt  with.  If  the  potatoes  have  been 
exposed  after  digging  there  is  a  possibility  that  there  will  be  eggs  on  the 
potatoes  treated,  and  a  fifth  application  of  carbon  bisulfid  becomes 
necessary.  This  fifth  treatment  should  be  given  at  the  end  of  the 
eighth  week  of  storage.  So  completely  successful  was  the  work  with  the 
bisulfid  that  in  none  of  the  experiments  where  it  was  used  did  a  single 
chrysalis  escape,  and  in  no  case  did  its  persistent  use  fail  to  stop 
infestation. 

REMEDIES. 

In  discussing  the  experimental  work  under  various  headings,  reme- 
dies have  been  noted  that  proved  successful  in  practice,  and  the  various 
recommendations  here  made  have  been  tested  under  working  conditions 
in  actual  practice.  Attention,  however,  must  be  drawn  to  the  fact  that 
in  any  case  of  infestation  there  comes  a  point  where  remedies,  that  at  one 
time  would  have  been  successful,  are  useless.  So,  in  handling  an  insect 
attack,  we  must  not  wait  until  the  insect  is  out  in  force  and  then  try  to 
rid  our  crops  of  the  pest,  but  the  fight  must  be  begun  when  the  invasion 
is  in  its  incipiency,  and  beginning  thus  we  may  confidently  expect  our 
efforts  to  lead  to  success.  The  farmer  who  carefully  watches  his  potato 
field,  and  is  ready  to  begin  the  battle  against  the  moth  when  it  first 
appears,  has  an  easier  fight  than  he  who  waits  until  the  full  army  of 
the  moth  is  in  array  against  him;  and  so  it  is  all  along  the  line  until 
the  potatoes  are  marketed. 

By  vigilance  and  watchfulness,  as  well  as  by  the  use  of  discrimina- 
tion in  suiting  the  remedy  to  the  conditions,  the  insect  may  be 
controlled,  even  in  the  localities  worst  affected. 


—  25  — 

Food  Plants  Should  Be  Destroyed. — As  has  been  before  stated,  the 
insect,  according  to  all  observations,  confines  itself  in  its  larval  form  to 
solanaceous  plants,  and  its  great  injury  is  done  among  the  cultivated 
representatives  of  this  family,  notably  in  the  potato  and  tobacco.  It 
has  been  reported  as  feeding  and  breeding  among  the  wild  members  of 
the  family,  and  this  feature  of  its  career  was  considered  of  value  in  this 
investigation,  because  if  any  of  these  wild  members  were  to  be  found 
near  the  cultivated  plants  they  would  constitute  a  good  breeding-place 
for  the  insect  and  a  point  for  infection  to  originate.  We  have  in 
California  much  of  the  so-called  "  night  shade,"  the  Solanum  Douglasii, 
S.  nigrum,  S.  umbelliferum,  and  S.  Xanti,  and  where  these  plants  are 
found  the  insect  is  sure  to  be  found  also,  as  collections  made  among 
and  near  them  have  shown.  Furthermore,  collections,  especially  at 
lights,  made  hundreds  of  feet  from  any  solanaceous  plants,  have  shown 
the  moth  to  be  present,  thus  indicating  its  ability  for  flying  quite  long  dis- 
tances. This,  together  with  the  fact  that  the  insects  are  not  confined  to 
the  cultivated  plants  of  the  family  Solanacese,  but  attack  the  wild  rep- 
resentatives also,  at  least  suggests  that  any  patch  of  such  plants  as 
the  night-shades  constitutes  a  menace  to  any  potato  plants  in  the 
neighborhood,  and  that  all  such  patches  should  be  destroyed. 

Light- Trapping. — It  has  been  noted  (p.  17)  that  the  moth  is  easily 
taken  in  large  numbers  at  lights,  and  in  the  use  of  light-traps  we  have 
a  most  effective  method  of  killing  it.  The  use  of  the  light-trap, 
too,  is  a  most  satisfactory  way  of  finding  out  whether  the  moth  has 
begun  to  work  in  a  potato  field,  as  two  or  three  such  lights  scattered 
about  the  field  will  surely  show  specimens,  if  any  are  flying.  If  the 
moth  is  found  to  be  present,  then  the  traps  might  be  placed  in  the  field 
at  intervals  of  100  feet  or  so,  and  kept  in  action  each  night  until  moths 
fail  to  be  taken  at  them.  It  seems  most  probable  that  the  persistent 
use  of  these  traps  at  this  time  will  greatly  reduce  the  possibilities  of 
infestation.  There  are  various  forms  of  these  traps  on  the  market,  and 
some  of  them  are  quite  effective,  though  probably  not  more  so  than  the 
common  lantern  trap,  made  by  soldering  a  torch  body  into  the  center  of 
a  shallow  pan  and  attaching  beneath  a  tin  ferrule,  by  which  it  is  sup- 
ported on  top  of  a  stake  driven  into  the  ground. 

Destroy  Infested  Stalks. — If  infestation  of  the  plants  has  begun  before 
note  has  been  made  of  the  presence  of  the  moth  in  the  field,  then  in 
addition  to  the  use  of  the  lights  suggested  above  it  would  without  doubt 
amply  pay  to  go  carefully  over  the  field  and  cut  off  the  infested  stalks 
just  below  where  the  injury  is  apparent,  and  remove  and  destroy  them 
(see  p.  20).  The  infested  plants  will  be  recognized  from  their  evident 
wilting,  and  this  work  can  be  done  quite  rapidly.     When  a  man  has 


—  26  — 

become  somewhat  expert  in  recognizing  the  trouble,  he  will  be  able  to 
remove  all  infested  stalks  from  a  row  in  about  twice  the  time  it  would 
take  him  to  walk  the  length  of  the  same  row.  The  object  of  this  work 
is  to  stop  the  infestation  before  it  becomes  general ;  but  it  is  evident 
that  much  watchfulness  is  required  in  detecting  the  attack  in  its  incip- 
iency.  If  the  plants  showing  stalk-infestation  are  not  too  young,  the 
removal  of  a  part  of  the  stalk  does  not  materially  hurt  the  plant  as  a 
tuber-producer.  If  the  infestation  is  noted  in  an  old  plant,  then  the 
whole  head  may  be  removed  a  short  distance  beneath  the  surface  of  the 
ground  a  week  or  ten  days  before  digging,  thus  effectively  disposing  of 
the  worms,  but  in  no  way  injuring  the  tubers  (see  p.  20).  The  neces- 
sity of  destroying  it  at  this  time  depends  upon  the  fact  that  the  worm 
may  either  come  out  from  its  burrow  and  pupate  and  then  transform  to 
the  moth  and  be  ready  to  multiply  the  damage  many-fold,  or  may 
leave  the  stalk  and  work  its  way  to  the  tubers  in  the  ground. 

Careful  Hilling. — One  of  the  most  effective  methods  of  preventing 
infestation  of  the  tubers  where  flat  culture  is  not  imperative,  is  to  be 
found  in  careful,  compact  hilling.  Too  often  in  our  large  potato  fields 
where  hilling  is  the  practice,  it  is  done  so  carelessly  that  many  of  the 
tubers  are  not  covered  completely,  or  if  covered  it  is  by  a  very  thin  and 
dry  layer  of  earth.  The  potatoes  that  are  not  completely  covered  are 
attractive  to  the  moth  and  are  almost  sure  to  be  infected,  while  those 
that  are  thinly  covered  may  be  easily  reached  by  the  worm  when  it 
leaves  the  stalk. 

If  the  covering  over  the  potatoes  in  the  hill  is  composed  of  lumpy 
material,  the  moth  itself  may  find  its  way  to  the  tubers,  and  infestation 
will  follow.  The  greatest  care  should  therefore  be  taken  in  this  matter 
of  hilling  if  the  moth  is  about,  as  experiment  has  shown  that  where 
careless  hilling  is  the  practice  great  damage  will  ensue  (see  p.  18). 
When  flat  culture  is  practiced  the  same  protection  of  the  tubers  should 
be  accomplished  by  deep  planting,  supplemented,  where  necessary,  by 
slight  hilling  at  the  last  cultivation. 

Avoid  Exposure  While  Digging  the  Potatoes. — The  potatoes  should  not 
be  exposed  to  a  possible  visit  from  the  moth  while  they  are  being  dug. 
The  moth  at  this  time  is  ready  for  the  potatoes  and  will  find  them  if 
they  are  exposed  for  any  great  length  of  time,  and  especially  if  they  are 
left  exposed  over-night.  The  practice  of  covering  the  newly-sacked 
potatoes  with  the  potato  tops  to  shade  them,  should  also  be  avoided, 
and  care  should  be  taken  to  remove  the  sacked  potatoes  within,  at  most, 
four  hours  after  digging.  If  such  removal  is  impossible,  then  the 
sacks  of  potatoes  should  be  stacked  in  the  field  and  covered  closely  with 
a  cloth  of  some  sort  to  ward  off  possible  visits  from  the  moth  (see  p.  19). 


—  27  — 

Clean  Up  the  Field  After  Digging. — The  old  heads  and  waste  potatoes 
should  be  destroyed  in  the  field  after  the  crop  has  been  removed,  espe- 
cially if  the  insect  is  at  all  in  evidence,  as  this  waste  material  offers 
a  good  breeding-place  for  the  moth  and  may  serve  to  carry  the  infesta- 
tion forward  to  the  next  crop  (see  p.  14).  The  most  satisfactory  way 
to  clean  up  a  field  of  any  large  size  is  to  turn  sheep  into  it  to  pasture. 
The  sheep  are  even  more  effective  in  their  work  than  hogs,  and  seem  to 
find  every  potato  in  the  field,  even  going  so  far  as  to  paw  up  any  tubers 
that  may  have  been  missed  in  the  digging  and  have  remained  covered 
with  earth.  In  cases  where  a  field  has  been  flooded  for  two  or  three 
weeks  the  infestation  seems  to  have  been  thoroughly  destroyed.  Any 
method  that  will  destroy  the  waste  potatoes  on  and  in  the  ground  will 
be  effective,  but  this  destruction  must  be  accomplished  if  the  ground  is 
to  be  used  for  potatoes  the  ensuing  year.  Where  this  cannot  be  done,  a 
rotation  of  crops  is  suggested  as  the  only  safe  means  of  procedure,  and 
it  is  effective  because  the  worm  feeds  solely  on  solanaceous  plants. 
Attention  is  here  again  called  to  the  fact  that  the  tubers  used  as  seed 
must  be  free  from  infestation,  as  the  moth  will  breed  from  such  infested 
potatoes  and  will  soon  overrun  the  field. 

Control  of  the  Moth  among  Stored  Potatoes. — The  attack  of  the  moth  is 
the  cause  of  great  loss  among  stored  potatoes,  and  it  is  probable  that  it  is 
the  damage  done  at  this  time  that  has  been  most  observed.  It  is  in  the 
storerooms  that  surrounding  conditions  can  be  most  easily  controlled, 
but  it  is  also  here  that  the  attack  is  most  concentrated,  and  therefore  at 
this  time  the  work  against  it  should  be  prosecuted  with  the  greatest 
vigor. 

Attention  has  been  called  to  the  use  of  carbon  bisulfid  (  see  p.  23  )  as 
an  effective  weapon  against  the  moth  when  it  is  in  the  chrysalis  form, 
and  the  careful  use  of  this  agent  will  undoubtedly  stop  the  infestation 
among  the  stored  tubers.  To  use  the  carbon  bisulfid  to  any  advantage 
the  tubers  must  be  placed  in  tight  rooms  or  bins  made  in  such  a  way  that 
when  the  gas  is  being  generated  little  or  no  leakage  may  occur.  A  bin 
made  of  tongue-and-groove  lumber,  with  a  top  cover  fitting  quite  closely, 
is  to  be  considered  the  best  for  disinfecting  small  quantities.  When 
larger  quantities  are  to  be  treated,  they  may  be  piled  in  a  tight  room; 
the  exact  dimensions,  the  cubic  space,  of  the  room  or  bin  must  be  known, 
as  the  amount  of  the  carbon  bisulfid  used  is  determined  by  this  cubic 
content. 

It  has  been  found  in  fighting  insects  in  stored  grain  that  one  pound 
of  the  bisulfid  to  one  thousand  cubic  feet  of  space  is  effective,  but  as 
potatoes  are  sacked  this  amount  had  better  be  increased  to  one  and  one 
half  (1^)  pounds,  on  account  of  the  large  air  spaces  occurring  between 
the  sacks.     As  far  as  our  experiments  go,  they  have  shown  that  the  gas 


—  28  — 

generated  diffuses  thoroughly  among  sacked  potatoes,  and  that  the 
chrysalids  are  killed  here  quite  as  well  as  when  the  tubers  are  not  sacked. 
Five  treatments  of  the  carbon  bisulfid  should  be  given  to  each  lot  of 
potatoes,  in  this  order:  A  treatment  when  the  tubers  are  first  stored;  a 
second,  third,  fourth,  and  fifth  treatment  at  intervals  of  two  weeks  (see 
p.  24).    In  a  room  or  bin  that  measures  10  feet  each  way,  we  have  1,000 


Fig.  8.    The  work  of  the  Flea  Beetle. 

cubic  feet  of  space,  which  will  hold  from  200  to  250  sacks  of  potatoes, 
and  five  thorough  treatments  of  the  contents  will  require  5  to  7-J  pounds 
of  the  carbon  bisulfid. 

The  material  should  be  placed  in  shallow  dishes  on  top  of  the  potatoes, 
and  then  all  should  be  tightly  shut  in.  The  liquid  carbon  bisulfid  be- 
comes a  gas  on  being  exposed  to  the  air,  and  this  gas  being  heavier  than 
the  air,  sinks  to  the  bottom  and  soon  fills  the  spaces  between  the  potatoes 


—  29  — 

with  its  poisonous  fumes.  The  gas  is  highly  inflammable,  and  the  greatest 
care  must  be  exercised  in  handling  it;  be  sure  that  no  lights  of  any  kind 
are  near  by  at  the  time,  or  the  results  will  be  disastrous.  The  gas  will 
kill  all  the  chrysalids  and  all  the  adult  moths  present  at  the  time,  and 
will  not  injure  the  tubers. 

OTHER    PESTS. 

In  the  course  of  this  investigation  of  the  moth  G.  operculella  and  its 
damages  to  the  potatoes  in  California,  certain  other  pests  have  been 
noted  as  causing  more  or  less  injury  to  this  crop,  and  we  briefly  sum- 
marize these  observations  here. 

Flea  Beetles. — In  the  experiment  plot  on  the  Station  grounds  some 
damage  was  done  to  the  plants  by  one  of  the  flea  beetles  {Epitrix  sub- 
crinita  Lee),  and  in  certain  of  the  fields  visited  the  damage  done  by 
another  representative  of  the  group,  E.  hirtipen- 
nis  Mels.,  was  quite  large.  These  insects,  which 
are  true  leaf-feeders,  belong  among  the  beetles 
in  the  family  Chrysomelidse.  They  are  minute 
(1.5  mm.  long),  generally  black  or  dark  brown, 
ochreous-tinted  beetles.  The  thoracic  region 
and  the  elytra  are  regularly  pitted.  The  pits 
are  the  seats  of  minute  hairs  (see  Fig.  9).  Their 
general  appearance  and  their  habit  of  jumping 
from  their  position  on  the  leaf  by  means  of  their 

,.,  -i-i«-ii  •      i  j  ien  Fig.  9.    Epitrix  hirtipennis  Mels. 

thickened  hmd  legs,  remind  one  strongly  of  a  ilea,    „,,..-*- 

°  3  D  J  '      Right  hand  figure  gives  ac- 

whence  the  common  name,  flea  beetles.     They  eat  tual  size  of  insect, 

small  round  holes  in  the  potato  leaf,  and  when  the  attack  is  severe  the 
leaves  become  so  riddled  with  the  punctures  as  to  be  able  to  function  as 
leaves  no  longer.  Figure  8  gives  a  good  idea  of  the  character  of  their 
work.  The  attack  on  the  field  from  which  the  leaf  here  figured  was 
taken  was  so  severe  that  the  value  of  the  crop  was  reduced  fully  50  per 
cent. 

As  stated  above,  this  beetle  is  a  leaf-feeder,  and  it  can  therefore  be 
controlled  by  the  use  of  Paris  green,  either  dusted  on  the  plant  or  used 
as  a  spray.  The  spraying  material  should  be  made  up  of  one  pound 
of  pure  Paris  green  to  one  hundred  and  fifty  gallons  of  water,  and  may 
be  cheaply  and  effectively  applied  to  the  plants  by  the  use  of  a  tank  and 
spray  pump  on  a  wagon.  The  spray  should  be  used  as  soon  as  the 
attack  is  observed,  and,  unless  it  is  very  violent,  one  application  will 
probably  be  found  sufficient  to  keep  the  beetles  below  the  danger  limit. 

Stenopelmatus,  incorrectly  called  Yellow  Ground  Cricket,  Sand  Cricket, 
Jerusalem  Cricket,  Common  Beetle,  and  Potato  Bug. 

There  are  frequently  noticed  in  the  potatoes  places  where  the  tubers 


—  30  — 

are  bitten  into  as  though  mice  had  been  gnawing  them.  These  wounds 
are  quite  evident  in  some  specimens,  and  render  the  tubers  attacked 
unmarketable  as  a  first-class  product  (see  Fig.  6).  The  insect  causing 
this  damage  is  a  large  and  clumsy  member  of  the  family  to  which  the 
katydids  belong.  It  has  a  large  and  horny  head  and  a  soft  and  heavy 
abdomen.  Its  movements  are  awkward  and  slow,  and  its  color  ranges 
from  yellow  to  brown.  It  never  has  wings.  It  will  be  at  once  recog- 
nized from  the  figure  No.  10.  These  insects  seldom  become  numerous 
enough  to  do  any  large  amount  of  damage,  but  nevertheless  they  should 
be  killed,  crushed,  wherever  found.  They  can  be  trapped  by  placing  bits 
of  board  upon  the  ground  in  the  field.  The  insects  get  beneath  these 
boards  and  may  be  easily  killed  there. 


Fig.  10.    Stenopelmatus. 


